1. Technical Field
The present invention relates to a synthetic resin bottle-type container obtained by molding a synthetic resin, such as polyethylene terephthalate, by biaxial stretch blow molding, and aims at advantageously avoiding occurrence of deformations of the container, particularly deformations on its shoulder portion due to dislocation of pressure reduction absorbing panels.
2. Prior Art
Currently, synthetic resin containers represented by PET bottles are widely used as containers for storing beverages, seasonings, liquors, detergents, medicines, etc., because they are light in weight and easy to handle, they ensure transparency to provide a refined appearance comparable to glass containers, and they can be obtained at low cost.
Moreover, for this type of synthetic resin containers, improvements have been achieved in terms of the heat-resistance so that the containers can be directly filled with relatively hot contents immediately after high-temperature sterilization, without requiring a previous cooling thereof.
Particularly in the case of such containers with improved heat resistance, deformations of the container takes place inevitably, due to reduction of the internal pressure upon cooling of the contents to the room temperature. In order to minimize such deformations, the container body may be provided with at least one groove that is recessed inwards of the container, to thereby define the so-called pressure-reduction absorbing panels.
However, when the containers having the pressure-reduction absorbing panels, particularly the containers of a rectangular cross-section, are provided with the border of the panels close to the shoulder portion, a local indentation of the shoulder portion tend to take place along with the dislocation of the panels upon absorption of the pressure reduction. The containers with locally indented shoulder portion cannot be shipped as marketable products, and thus cause the yield to be lowered.
In the synthetic resin blow molded containers, the shoulder portion has a relatively poor strength since, from the beginning, the wall at the shoulder portion tends to become thin, and the wall itself does not undergo a sufficient stretching as is the case with the container body portion. In this connection, there has been proposed a blow-molded container provided at its shoulder portion with a stepped portion, and the region extending from the stepped portion to the container body portion has a polyhedral shape as defined by triangular panels (see, for example, Japanese Patent Application Publication No. 06-127542). However, due to the progressive demand for the weight reduction of resin containers and a resultant reduced wall thickness at the shoulder portion, large-sized containers with a volume of as large as 1.5 l tend to be severely affected by the dislocation of the panels due to an increased absorption amount of the pressure reduction. Thus, a mere application of the conventional approach would not provide a sufficient solution.